It is an accepted surgical procedure to install devices known as intramedullary nails in order to stabilize femoral and tibial fractures. The surgical technique of repairing such a fracture includes installing a prosthetic device known as an intramedullary nail in the medullary canal of the bone and locking it in place by means of self-tapping screws driven through holes located at both the distal and proximal ends of the nail for anchoring the nail in the surrounding bone.
This type of intramedullary fixation has been found effective for proximal and distal third shaft fractures, severely comminuted spiral and segmental fractures, non-unions and malunions between adjacent bone sections and bone lengthening where the fracture involves bone loss. By anchoring the intramedullary nail at both ends, the tendency for portions of the bone on adjacent sides of the fracture to rotate relative to each other is prevented and the length of the bone is maintained.
When a patient has a fracture complicated enough to require an interlocking intramedullary nail, the patient is positioned properly and an incision is made near the proximal end of the bone. The medullary canal is reamed and the intramedullary nail is introduced using known techniques.
The intramedullary nail is inserted into the bone, the nail being large enough to completely fill the intact medullary canal. A typical nail has two screw holes in its distal end and one in its proximal end so that self-tapping screws can be inserted for anchoring the nail to the bone. As can be appreciated, once the intramedullary nail has been installed in the bone, these holes cannot be visually observed by the physician and they must be located before the screws can accurately be inserted through the surrounding bone. An accepted technique for inserting the screw at the proximal end is to mount a fixture on the exposed end of the intramedullary nail with a drill guide that is aligned with the hole in the nail so that a guide hole can be drilled through the bone, through which the screw is inserted. Since the proximal screw hole is relatively close to the proximal end of the nail, this procedure is relatively uncomplicated.
However, for the two blind holes at the distal end of the nail, their distance from the proximal end is sufficiently great that it is difficult to locate them accurately. The importance of accurate location is apparent since before a locking screw can be inserted through these holes, a hole has to be drilled in the bone. Accurate location is therefore important to prevent trial and error location of the blind holes and unnecessary holes in the bone, which cause apparent problems.
Several techniques have been developed for locating these blind holes so that a guide hole can be accurately drilled in the bone for insertion of locking screws. All of these techniques involve the use of X-ray machines so that the physician can determine where the hole is located relative to the outer surface of the patient's leg. The difficulty of accurately locating the holes so that an incision can be made and an accurately located guide hole drilled in the bone is to determine the correct orientation of the blind hole relative to the outer skin of the patient. This problem is exacerbated by the fact that X-ray machines are two-dimensional so that even though the blind hole appears on an exposed X-ray plate, the physician cannot be certain of the axial orientation of the blind hole. If the guide hole is not co-axial with the blind hole axis, the anchoring screw cannot fit through the blind hole in the nail.
A serious problem in connection with locating these blind holes involves the fact that for each of these techniques a physician must be exposed to radiation from the X-ray machine while attempting to locate the holes. Overexposure to such radiation is dangerous to the physician and if a physician is exposed beyond predetermined safe levels, he or she would have to curtail the number of operations or stop operating on these types of fractures or face the possibility of serious health risks. Although lead-lined gloves have been developed for shielding the physician's hand and arm from harmful radiation, these are bulky and clumsy to use and many physicians believe that they hamper the physician's tactile effectiveness in performing the operation.
One technique that has been used for locating these blind holes in the distal end of an intramedullary nail is called a free-hand technique where the tip of a surgical instrument such as an awl is centered over the hole as determined with the aid of an X-ray machine. The shaft of the awl is moved until it is aligned with the X-ray beam while maintaining the tip of the awl in its original location at the opening of the hole. It has been found that this free-hand technique is not consistently accurate because the surgeon's hand oftentimes moves, especially when the awl is in contact with the slippery sloped surface of exposed bone. More importantly, however, is that the surgeon's hand is at times directly within the X-ray beam. Unless a surgeon is particularly skilled and can locate the axis of the blind hole quickly, overexposure to radiation can be a significant problem. Additional extension instruments have been developed to allow the surgeon to maintain the position of the awl through remote manipulation, but these extensions add additional instability to the system. Further, after the hole in the distal end of the intramedullary nail is located it must often times be relocated for drilling and screw insertion. This adds extra time to the operation.
A second technique has been developed that uses a targeting device that is fixed at the proximal end of the intramedullary nail and includes an arm that extends generally parallel to the nail. The arm has a joint in it so that it can pivot relative to the nail. However, the lever arm is relatively long and deflection can occur, which does not allow for precise location of the axis of the blind hole. Although the axis of the hole can be determined, there is some trial and error involved since the technique does not involve a predetermined sequence of steps; instead, the motions are complex with several degrees of freedom being manipulated simultaneously. Thus, unless a surgeon is particularly skilled, this procedure can be time consuming.
A third technique involves the use of a targeting device located on the C-arm of an X-ray machine. This device enables the surgeon to locate the axis of the screw hole, but there is no provision for a fine adjustment and the entire C-arm must be moved in order to accurately locate the hole, which is awkward in an operating room.